Well,recently,I encountered a problem. I was MTing Karazhan,and we reached the room after Curator(Before Aran,where the Journal of Medivh quest is).I was terrified of the fact that the mobs there are magic immune,since as a Paladin tank,I can't generate threat with just physical power. Luckily enough,my druid Off Tank picked them up for me,and got the whole deal done,while I was standing aside,shamed that I could not have helped the group.
This leads to my question:
A) Are immunities same as resistances for mobs? Would spell penetration of any kind would help?
B)Although they don't hit hard,they still do hit.If I can't control agro,it means damage on DPS and healers,but all of our mages and warlocks couldn't do a think in that situation,for the very same reason.
How is this situation solved without a full physical team,or a non magic using tank?
A) Immunities are different than resistances. Spell penetration will not help against immunities.
B) In general, don't worry about it. These mobs don't hit hard enough to make it an issue. Your hunters, warriors, rogues, shamans can help tank these things. Just get everyone (including the mages/warlocks) in there whacking away with their weapons.
As well, you should use Seal of the Crusader when attacking the mobs. You still get threat from white damage, though not a whole lot. SotC will increase your white damage. Tab-target to hit different mobs. It should be enough threat to keep them off the healers.
Basically, no one should stand aside on these mobs. Just attack them with your physical attacks, focus fire, and they'll go down quickly.